Semiconductor optical device with beam focusing

ABSTRACT

An integrated optical device formed in a semiconductor substrate incorporated an integral lens element in the substrate for providing focusing of the output beam. The device includes an optically active region for generating and confining optical radiation and having an output end for emitting an output beam from the optically active region; and a lens region adjacent the output end which has an increased band gap to the adjacent substrate material and is shaped to provide a lens effect on said output beam. The optically active region forms a cavity having a longitudinal axis, and the lens region extends along the longitudinal axis and has a lateral extent that varies as a function of distance along the longitudinal axis.

The present invention relates to semiconductor optical devices, and inparticular to optical output structures for such devices.

An edge emitting semiconductor laser device generally emits anelliptical far-field optical output with a typical vertical tohorizontal aspect ratio of approximately 3:1. Therefore, coupling theelliptical output of an edge emitting laser into a glass fibre or otheroptical waveguide is typically not very efficient.

For example, butt coupling a laser against a glass fibre or waveguidetypically gives a coupling efficiency of approximately 30%. The farfield of the laser can be further reduced to slightly improve thecoupling efficiency using a number of structures generally known in theart, but this is usually at the expense of other laser parameters suchas threshold.

The problem is particularly acute for single-mode optical coupling wherecoupling efficiencies are particularly sensitive to misalignment due tothermal cycling or vibration in the assembled, coupled device.

To improve the coupling efficiency, the prior art generally suggests theuse of a lens (or a system of lenses) that can be adopted to collect andfocus the laser light into the optical fibre or waveguide. In the idealcase, a system of lenses (for example, up to four lenses) is required toadjust the laser output from an elliptical profile to a circular profileand focus the output beam to a tight spot.

However, a system of lenses is often impractical. There are numerousdifficulties and additional costs in packaging the assembled device andusually cost is an important factor for many applications.

Alternatively, a commonly adopted solution in the prior art is toprovide a single lens element machined onto the end of the opticalfibre, onto which the laser beam is directed, giving a couplingefficiency of up to approximately 80%. However, this system cannot beeasily adapted to other types of optical waveguides (eg. thoseintegrated onto a semiconductor substrate) and is expensive. Asintegration on chip becomes important, the number of devices on chip,the footprint and the cost are important issues, and lens fibre becomesprohibitively expensive and bulky.

In another prior art solution, free space coupling may be achieved. Forexample, a holographically etched or anamorphic lens can be used toachieve coupling efficiencies of the order of 60%. Arrays of microlenseshave been considered for coupling arrays of lasers into waveguidearrays. The laser light is directed onto a standing lens and thenfocused into the fibre or waveguide, resulting in two air gaps andtherefore lower efficiency. However, complicated packaging solutions arerequired to achieve such coupling efficiencies in a manufacturedproduct.

It is therefore desirable to provide a semiconductor laser or otheroptical device having an optical output that can be efficiently coupledinto an optical fibre or other optical waveguide without the need for anexternal lens.

According to one aspect, the present invention provides an integratedoptical device comprising a semiconductor substrate in which is formed:

an optically active region for generating and confining opticalradiation and having an output end for emitting an output beam from theoptically active region;

a lens region positioned to receive the output beam from the output end,the lens region having a reduced refractive index and/or an increasedband gap to adjacent substrate material and being shaped to provide alens effect on said output beam.

According to another embodiment, the present invention provides a methodof forming an integrated optical device comprising the steps of:

forming an optically active region for generating and confining opticalradiation in a semiconductor substrate, the optically active regionhaving an output end for emitting an output beam from the opticallyactive region; and

forming a lens region in the substrate positioned to receive the outputbeam from the output end, the lens region having a reduced refractiveindex and/or an increased band gap to adjacent substrate material andbeing shaped to provide a lens effect on said output beam.

Embodiments of the present invention will now be described by way ofexample and with reference to the accompanying drawings in which:

FIG. 1 a is a schematic perspective diagram of a conventionalsemiconductor laser device having an elliptical optical output andhaving quantum well intermixed regions adjacent the end facets to reducethe risks of catastrophic optical damage;

FIG. 1 b is a cross-sectional view on line A-A of FIG. 1 a;

FIG. 2 is a schematic plan view of a semiconductor laser device havingan integrated optical lens at an output facet of the device;

FIG. 3 is a schematic plan view of a device similar to that of FIG. 2,illustrating the optical focusing effects of the integrated opticallens;

FIG. 4 is a graph illustrating the variation in refractive index againstoptical wavelength, in Ga_(1-x)Al_(x)As, as a function of the Ga:Alratio, x;

FIG. 5 is a schematic cross-sectional side view of a semiconductor laserdevice having an integrated optical lens formed by a thickness gradedlayer of silica on the device surface;

FIG. 6 is a schematic diagram showing the band gap resulting fromquantum well intermixing by thermal annealing of the structure of FIG.5;

FIG. 7 is a schematic cross-sectional side view of a layeredsuperlattice structure suitable for forming an integrated optical lens;

FIG. 8 is a schematic diagram of the band gap resulting from thestructure of FIG. 7;

FIG. 9 is a schematic cross-sectional side view of a layeredshort-period superlattice structure suitable for forming an integratedoptical lens;

FIG. 10 is a schematic diagram of the band gap resulting from thestructure of FIG. 9;

FIG. 11 is a schematic cross-sectional side view of a graded band gap,layered superlattice structure suitable for forming an integratedoptical lens;

FIG. 12 is a schematic diagram of the band gap resulting from thestructure of FIG. 11;

FIG. 13 is a schematic perspective view of a semiconductor laser devicehaving an integrated, three dimensional optical lens structure; and

FIG. 14 is a schematic side view of a vertical cavity surface emitterdevice incorporating an integrated optical lens at its output facet.

Referring firstly to FIGS. 1 a and 1 b, there is shown a conventionalsemiconductor laser device, generally designated 1, suitable formodification in accordance with the present invention. The device 1comprises an optical ridge waveguide 2 and at least one electricalcontact 3 extending along part of the length of the waveguide 2.

One end 4 of the electrical contact 3 is spaced from a respective end 5of the optical waveguide 2. As shown, the optical waveguide 2 is a ridgewaveguide laterally bounded by etched portions 6 a, 6 b, and theelectrical contact 3 is provided along the top of the ridge waveguide.However, other types of waveguide and contact are known, which are alsoapplicable to the present invention. For example, the etched portions 6a, 6 b may comprise compositionally disordered or quantum wellintermixed portions bounding sides of the optical waveguide 2.

An optically active or gain region 7 lies beneath optical waveguide 2.An optically passive region 8 a, 8 b is provided at each end of theoptical waveguide. Generally, the optically passive regions 8 have awidth the same as the waveguide, as shown at 8 a, the non-output end ofthe optically active region in FIG. 1 a. In some circumstances, theoptically passive region 8 b may be broader than the optical waveguide 2so that, in use, an optical output of the optical waveguide 2 diffractsas it traverses the optically passive region 8.

In this way, the optical output is expanded so that the intensity oflight impinging on an output facet 9 of the device 1 is reduced, therebyreducing the risk of catastrophic optical mirror damage.

The optically active and passive regions 7, 8 are provided within anoptical guiding or core layer(s) 10 between first and second (lower andupper) optical cladding confining layers 11, 12. Typically, the firstcladding layer 11 and the second cladding layer 12 each have arefractive index that is lower than that of the guiding layer(s) 10 toprovide waveguiding properties.

The ridge waveguide 2 is formed in at least the second cladding layer 12and extends longitudinally from the first end 5 of the device 1 to aposition 13 between the first end 5 and a second end 14 of the device10. The second end 14 comprises an output of the semiconductor laserdevice 1. The output facet may include an anti-reflective coating which,in combination with the passive region 8 b, provides a non-absorbingmirror.

The optical guiding (core) layer(s) 10 comprise an active lasingmaterial layer including a Quantum Well structure. The optically passiveregions 8 a, 8 b include a compositionally disordered semiconductormaterial provided within the guiding layer 10, having a larger band-gapthan the guiding layer 10.

The device 1 is of a monolithic construction including a substrate 15,upon which the other layers may be grown by conventional III-Vsemiconductor growth techniques, eg Molecular Beam Epitaxy (MBE) orMetal Organic Chemical Vapour Deposition (MOCVD). The compositionallydisordered lasing material may be achieved through Quantum WellIntermixing (QWI) according to known techniques.

The semiconductor laser device may be fabricated in a Gallium Arsenide(GaAs) materials system such as Aluminium Gallium Arsenide (AlGaAs)material system, and may therefore lase at a wavelength of between 600and 1300 nm, and preferably around 980 nm. The guiding layer 10 maysubstantially comprise in Indium Gallium Arsenide (InGaAs).Alternatively, the device 10 may be fabricated in an Indium Phosphide(InP) materials system, eg operating in a wavelength range of 1200 to1700 nm.

In accordance with the present invention, the laser device describedabove may be modified to provide a focusing element. As shown in theplan view of FIG. 2, a semiconductor laser device 20 includes a ridgewaveguiding structure 21 which effectively defines a longitudinal axis(x) of the optical device 20, and in particular defines a longitudinalaxis of the optically active region or cavity of the laser device. Atone end 22 of the optically active region there is formed anon-absorbing mirror 23 which preferably reflects substantially all ofthe optical radiation generated within the cavity.

The non-absorbing mirror 23 is preferably formed using a quantum wellintermixing process to locally increase the band gap of thesemiconductor substrate using techniques known in the art. An advantageof impurity free quantum well intermixing techniques to formnon-absorbing mirrors is that they allow the band gap to be increased atthe facet ends of a semiconductor laser to avoid catastrophic opticaldamage to the facet allowing the formation of high power, long lifetimedevices. However, other mirror structures could be used also as knownwithin the art.

At the output end 24 of the laser device 20 there is formed a lensregion 25 within the substrate and/or one or more of the opticalcladding/guiding layers thereon, which will all be referred tohereinafter as “substrate”. The lens region 25 is adapted to provide afocusing effect on the radiation emitted from the laser device andcomprises a region of substrate having a reduced refractive index fromthe adjacent substrate, and in particular relative to the opticallyactive region or cavity.

To this end, the lens region 25 is preferably defined as a shapedquantum well intermixed (QWI) region of larger band gap. The shapedprofile of the lens region is any suitable shape that provides afocusing effect on the output beam. The focusing effect may be used toenable the beam shape to be adapted for better coupling into an opticalfibre or any suitable waveguide structure (not shown).

In one arrangement as shown, the lens region 25 extends along thelongitudinal (x) axis and has a lateral extent (ie. a width and/or adepth) that varies as a function of distance along the longitudinalaxis, x. As described throughout the present specification and shown inthe drawings, the expression “width” refers to the dimension along the yaxis (as shown in FIG. 2), and the expression “depth” refers to thedimension along the z axis, into the substrate (as best shown in FIG.5).

More particularly, in the preferred embodiment, the variation in lateralextent of the lens region as a function of distance along thelongitudinal axis defines a curved profile to produce the requiredfocusing effect. A single step change in width of the waveguide, as isprovided in the prior art arrangement of FIG. 1 a does not result in afocusing effect.

In the preferred embodiments, the lens region 25 is formed using quantumwell intermixing (QWI) to locally increase the band gap and therebydecrease the refractive index of the substrate. More preferably, the QWIprocess used can be an impurity free QWI process. Use of a QWI techniqueto form the integrated lens region in the substrate enables theachievement of superior spatial resolution not available with othertechniques for locally modifying refractive index in the substrate. Inaddition, the preferred impurity free QWI process avoids introduction ofimpurities into the substrate which would otherwise cause opticalabsorption which can catastrophically damage the facet and hence giverise to device failure.

The shaped lens region 25 at the output facet 24 both avoidscatastrophic optical damage in the device and provides the requisitelens effect on the output beam to improve the coupling efficiency.

The formation of the lens region 25 integrated into the same substrateas the laser cavity can be effected in a straightforward manner usingQWI processing techniques and this avoids the need for a free space lenscoupling system between the laser and optical waveguide or fibre. Thismay offer many benefits, including substantial cost savings, reductionin the complexity of the packaging, facilitation of relaxed alignmenttolerances, improvement in yield and also in device lifetime.

As will be described in the following embodiments, the lens region maybe adapted to perform focusing of the beam in one or both of thehorizontal and vertical axes. The lens shaping may also reducecavity-coupling effects that can occur due to quantum well intermixingand hence improve the spectral output of the laser.

The use of an impurity free quantum well intermixing process isparticularly suitable for increasing the band gap (ie. decreasing therefractive index) in a controlled manner.

As shown in FIG. 2, in the preferred embodiment, the lens region 25 isformed by photolithographically defining a radius of curvature 26 in asilica layer deposited over the substrate during the QWI process. Athermal anneal process is then used to achieve the desired intermixingof the quantum well region, and hence reduction in refractive index. Bythis process method, the horizontal component of the output beam can bebrought to a focus, due to refraction at the curved surface 26. Thefocal length is determined by the radius of curvature and refractiveindex difference between the intermixed region 25 and the non-intermixedregion 27. By analogy to simple lens design, a plano-convex lens can befabricated.

The expected focusing effect is shown in FIG. 3. In this example, theridge laser 30 has a ridge width dimension of approximately 2 microns torestrict the transverse mode to single mode. At the output facet end 31of the device 30, the intermixed region 32 has a spherical surface 34with a radius of curvature of approximately 20 microns. The area withinthe radius of curvature is intermixed to increase the band gap byapproximately 100 meV in, for example, a 980 nm laser consisting mainlyof Al_(0.32)Ga_(0.68)As. A 100 meV increase in the AlGaAs band gap isequivalent to increasing the Al mole fraction by approximately 10%. A100 meV increase in the AlGaAs band-gap due to QWI corresponds to arefractive index change of approximately 2.2%.

A wavefront is generated in the active region 33 of the device 30 and isrefracted at the spherical surface 34 of radius R at the intermixedregion 32. A ray 35 from point s incident at an angle to the radius ofcurvature is refracted at an angle and intersects at a focus point P ata distance s′. The small-angle approximation gives a simple formula forimage formation by a spherical refracting surface as:n/s+n′/s′=(n′−n)/Rwhere n is the refractive index of the non-intermixed region 33, s isthe focal point within the optically active cavity, n′ is the refractiveindex of the intermixed region 32, s′ is the focal point outside theoutput facet and R is the radius of curvature of the lens region surface34.

Thus, for the example of R=20 microns, and a refractive index of n=3.23for the non-intermixed semiconductor and n′=3.16 for the intermixedregion of semiconductor, and for a cavity length to the non-absorbingmirror 23 of s=100 microns gives a focus at s′=110 microns. Thiscalculation gives a first approximation for the focal length and doesnot include a factor for the semiconductor/air interface, which canreadily be factored into the calculation if necessary.

The semiconductor laser 20, 30 can also be designed to include layers ofAlGaAs in the substrate with a higher aluminium mole fraction so thatthe refractive index contrast is greater and hence a larger focusing canbe obtained. FIG. 4 illustrates how the refractive index changes withband gap for different stoichiometric ratios of Ga to Al.

The foregoing example illustrates how the lens region 25, 32 may vary inwidth as a function of distance along the longitudinal axis x, the widthbeing defined as the axis orthogonal to the longitudinal axis andparallel to the surface of the substrate (shown as they axis).

Alternatively, and/or in addition, the refractive index of the lensregion can also be adapted to vary in depth as a function of distancealong the longitudinal axis, the depth being defined as the axisorthogonal to both the longitudinal axis and the surface of thesubstrate. This can be achieved by grading the refractive index in thecrystal growth direction, by selectively grading the degree ofintermixing, to give an index radius of curvature in the vertical (z)direction.

In one embodiment as shown in FIG. 5, the selective grading ofintermixing can be achieved by depositing a layer of silica 41 followedby thickness grading the layer of silica to form a “staircase” 42. Thethickness grading can be achieved by photolithographic masking andetching of the silica layer 41. The device is then thermally annealedunder optimum conditions for intermixing to give a graded band gap, asshown in FIG. 6.

The band gap shift 51 is determined in part by the depth of theoverlying silica layer 41 during the intermixing process. Thus, in thismanner, a radius of curvature in refractive index change can be achievedaccording to the band gap variation.

With reference to FIGS. 7 and 8, a further embodiment of optical device70 increases the optical overlap (ie. the extent to which the opticalfield extends into the cladding region), and hence the refractive indexcontrast, by way of a superlattice structure 71, 72 in the claddingregions of the device. In this arrangement, the cladding regions 71, 72are formed with a plurality of layers of semiconductor material in whichthe refractive index varies periodically in the z direction. Preferably,the plurality of layers comprise alternating layers 73, 74 of AlGaAs andGaAs respectively.

Preferably, the quantum well active region 75 is sandwiched on each sideby a graded index GRINSCH structure 76. The GRINSCH structure 76 andsuperlattice structure 71, 72 provide enhanced spatial confinement ofthe output beam.

Following a suitable anneal process, the quantum well intermixingresults in a refractive index change 77 in a staircase profile as shown.

To improve carrier injection into the active region and thereby achievea higher efficiency device, the AlGaAs band-gap can be aligned such thattransport through the AlGaAs X-band can be achieved, using techniquesknown in the art.

With reference to FIGS. 9 and 10, in a further arrangement, ashort-period superlattice 91, 92 is formed such that band overlapbetween superlattice layers creates a mini-band allowing transport ofcarriers and hence a low resistance device.

The short period superlattice 91, 92 is formed with a plurality oflayers 93, 94 of semiconductor material in which the refractive indexvaries periodically in the z direction. Preferably, the plurality oflayers comprise alternating layers 93, 94 of AlGaAs and GaAsrespectively.

Preferably, the quantum well active region 95 is sandwiched on each sideby a graded index GRINSCH structure 96. The GRINSCH structure 96 andsuperlattice structure 91, 92 provide enhanced spatial confinement ofthe output beam.

Following a suitable anneal process, the quantum well intermixingresults in a refractive index change 97 in a staircase profile as shown.

With reference to FIGS. 11 and 12, in a further arrangement, asuperlattice 111, 112 comprises a plurality of graded layers 113, 114such that band gap maxima of the periodic band gap (and thus the minimaof the refractive index) vary as a function of the z direction.

Preferably, the plurality of layers comprise alternating layers 113, 114of AlGaAs and GaAs respectively, in which the stoichiometric ratio ofthe AlGaAs varies to provide the variation in band gap maxima.

Preferably, the quantum well active region 115 is sandwiched on eachside by a graded index GRINSCH structure 116. The GRINSCH structure 116and superlattice structure 111, 112 provide enhanced spatial confinementof the output beam.

Following a suitable anneal process, the quantum well intermixingresults in a refractive index change 117 in a staircase profile asshown.

With reference to FIG. 13, it will be understood that both thevariations in depth and in width of the refractive index can be combinedin one structure to obtain an index radius of curvature in both the x-yplane (Δn boundary 131) and in the x-z plane (Δn boundary 132) to give athree dimensional plano-convex lens shape within the substrate and/orcavity. The radius of curvature is chosen for the particular opticalcoupling requirement.

Although the preferred embodiments describe an edge emittingsemiconductor laser device, the principles of the integrated lens regionat an output end of the device can be applied also to vertical cavityemitters such as vertical cavity surface emitting lasers (VCSELs) orresonant cavity light emitting diodes (RCLEDs).

FIG. 14 illustrates an exemplary vertical cavity emitter 140 which hasan active region 141 sandwiched between two mirrors (one of which isshown at 142) to create a microcavity. The output beam 143 from avertical cavity structure is generally spherically divergent. Thepresent invention allows collimate or focusing of the output beam from avertical cavity device as shown, eg. to a focal point 144. The surfaceregion 145 of the VCSEL or RCLED device 140 is provided with a gradedindex region 146 which varies in width as a function of distance alongthe longitudinal axis which axis is, in the case of a vertical emitter,in the vertical direction indicated as z in FIG. 14. This focuses theoutput light in either or both the x and y directions.

In the preferred embodiments described above, the lens region 25 (or146) is preferably immediately adjacent to the optically active regionstructure 21 (or 141), ie. the two structures share a common boundary.However, it is possible that the two structures could be separated bysome intermediate waveguiding structure, which may be optically passiveor active. Regardless of the nature of any intermediate waveguidingstructure, the optical output beam of the optically active region isdirected into the lens region.

In the preferred embodiments described above, the lens region 25 (or146) is preferably entirely optically passive. However, the lens regionmay also comprise an optically active structure, providing that arefractive index profile is maintained to produce the required focusingeffect.

Other embodiments are intentionally within the scope of the accompanyingclaims.

1. An integrated optical device comprising a semiconductor substrate inwhich is formed: an optically active region for generating and confiningoptical radiation and having an output end for emitting an output beamfrom the optically active region; a lens region positioned to receivethe output beam from the output end, the lens region having a reducedrefractive index and/or an increased bandgap to adjacent substratematerial and being shaped to provide a lens effect on said output beam.2. The device of claim 1 in which the optically active region forms acavity having a longitudinal axis, the lens region extending along thelongitudinal axis and having a lateral extent that varies as a functionof distance along said longitudinal axis.
 3. The device of claim 2 inwhich the depth of the lens region varies as a function of distancealong the longitudinal axis, the depth being defined as the axisorthogonal to both the longitudinal axis and the surface of thesubstrate.
 4. The device of claim 2 in which the width of the lensregion varies as a function of distance along the longitudinal axis, thewidth being defined as the axis orthogonal to the longitudinal axis andparallel to the surface of the substrate.
 5. The device of claim 4 inwhich both the depth and width of the lens region varies as a functionof distance along the longitudinal axis, depth being defined as the axisorthogonal to both the longitudinal axis and the surface of thesubstrate.
 6. The device of claim 1 in which the lens region is anoptically passive region.
 7. The device of claim 1 in which the lensregion includes an optically active structure.
 8. The device of claim 1in which the optically active region and the lens region are immediatelyadjacent one another.
 9. The device of claim 1 further including anintermediate waveguiding structure between the output end of theoptically active region and the lens region.
 10. The device of claim 3in which the lens region comprises a quantum well intermixed region, thedegree of quantum well intermixing varying as a function of distancealong the longitudinal axis.
 11. The device of claim 10 furtherincluding a layer of material of varying depth over the lens region, thematerial enhancing quantum well intermixing in the substrate material inwhich the lens is formed.
 12. The device of claim 1 further including asuperlattice structure having a periodic variation in refractive indexalong an axis orthogonal to the surface of the device, the superlatticeextending through the optically active region and the optically passiveregion.
 13. The device of claim 12 in which the superlattice structurefurther includes band overlap between layers within the superlattice tocreate a mini-band for transport of carriers.
 14. The device of claim 12in which the superlattice structure further provides a variation inperiodic band gap maxima as a function of distance along an axisorthogonal to the surface of the device.
 15. The device of claim 1 inwhich the optical device is a laser.
 16. The device of claim 15 in whichthe optical device is an edge emitting laser.
 17. The device of claim 1in which the device is a vertical cavity emitter having a cavity whoselongitudinal axis extends substantially orthogonally to the surface ofthe device.
 18. The device of claim 17 in which the lens region isformed in a surface layer of the device.
 19. A method of forming anintegrated optical device comprising the steps of: forming an opticallyactive region for generating and confining optical radiation in asemiconductor substrate, the optically active region having an outputend for emitting an output beam from the optically active region;forming a lens region in the substrate positioned to receive the outputbeam from the output end, the lens region having a reduced refractiveindex and/or an increased bandgap to adjacent substrate material andbeing shaped to provide a lens effect on said output beam.
 20. Themethod of claim 19 in which the step of forming the lens regioncomprises the steps of: depositing a layer of material onto thesubstrate, the material being adapted to enhance or suppress quantumwell intermixing in an underlying semiconductor substrate;photolithographically defining said material to provide a quantum wellintermixing cap having a lateral extent that varies as a function ofdistance along a longitudinal axis of said optically active region;thermally annealing the substrate to locally modify the band gapaccording to the extent of the deposited material.
 21. The method ofclaim 19 in which the step of forming the lens region comprises the stepof: depositing a layer of material onto the substrate, the materialbeing adapted to enhance or suppress quantum well intermixing in anunderlying semiconductor substrate; photolithographically defining saidmaterial to provide a quantum well intermixing cap having a layerthickness that varies as a function of distance along a longitudinalaxis of said optically active region; thermally annealing the substrateto locally modify the band gap according to the extent and depth of thedeposited material.
 22. The method of claim 21 in which the depth of thelens region varies as a function of distance along the longitudinalaxis, the depth being defined as the axis orthogonal to both thelongitudinal axis and the surface of the substrate.
 23. The method ofclaim 20 in which the width of the lens region varies as a function ofdistance along the longitudinal axis, the width being defined as theaxis orthogonal to the longitudinal axis and parallel to the surface ofthe substrate.
 24. The method of claim 21 in which both the depth andwidth of the lens region varies as a function of distance along thelongitudinal axis.
 25. The method of claim 19 in which the step offorming the lens region further comprises forming said lens region as anoptically passive region.
 26. The method of claim 19 in which the stepof forming the lens region further comprises forming at least part ofthe lens region as an optically active region.
 27. The method of claim19 further including the step of forming the optically active region andthe lens region immediately adjacent one another.
 28. The method ofclaim 19 further including the step of forming an immediate waveguidingstructure between the output end of the optically active region and thelens region.
 29. The method of claim 25 further including the step offorming a superlattice structure having a periodic variation inrefractive index along an axis orthogonal to the surface of the device,the superlattice extending through the optically active region and theoptically passive region.
 30. (canceled)